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Anatomy > Lecture 13 > Flashcards

Lecture 13 Flashcards

1
Q

Reis Bucklers dystrophy has what characteristic trait?

A

cornea is hazy centrally and not clear

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2
Q

what are the three major layers in the cornea? how many layers in total?

A

epithelium, stroma and endothelium.

5-6 layers.

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3
Q

What are the two outer most layers of the eye?

A

sclera and cornea.

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4
Q

Sclera is composed of what components?

A

fibroblasts, collagen, elastin fibres and PGs and is 70% water.

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5
Q

what is the sclera opaque?

A

because of irregular collagen fibres and high water content.

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6
Q

is the sclera vascular or avascular?

A

avascular EXCEPT for superficial vessels.

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7
Q

does the sclera have sensory endings?

A

NO therefore when you poke sclera it probably would not hurt.

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8
Q

What type of collagen is present in the sclera? and what does each type do?

A

90% made up of type 1 (larger diameter in the cornea, type one allows for resisting tension). type 3 (allows for expansion) and type 4 controls fibril dimensions.

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9
Q

What types of cells are present in cornea stroma?

A

VERY FEW, often considered acellular however, keratocytes can be present (fibroblasts) and collagen.

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10
Q

What gives the cornea transparency?

A

very organized arrangement of collagen fibres. arrangement of fibres depends on size and how close the fibres are to one another, small and ordered is the best for transparency. more space between cells allows for light to pass through easier.

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11
Q

What is the dua layer?

A

newly discovered, located in cornea very close to decemets membrane, dense layer of cells and the function is unknown.

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12
Q

The power of the cornea is what? typical curvature of the cornea? RI is usually what in the cornea?

A

43 D.
7-8mm
1.5

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13
Q

What is the RI of collagen fibres in the cornea? GAGs? water? what helps maintain constant water levels in the cornea?

A

1.55, 1.35 (causes some scattering), 1.33

pumps, fluid and ion barriers.

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14
Q

Is the cornea able to regenerate?

A

YES. by controlling fibroblast activation.

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15
Q

Corneal epithelium is involved in what two major functions of the cornea?

A

transparency and wound healing.

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16
Q

The transepithelial potential in the cornea is what?

A

25-35mV (this spreads through gap junctions and is maintained by pumps).

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17
Q

Is the inside of the cornea more positive or negative compared to outside?

A

inside is more negative and outside is more positive. therefore, positive ions want to move inside the cornea and negative ions want to move outside. this is controlled by ion channels which are controlled by the sympathetic system

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18
Q

What are the five different pumps on the basolateral membrane involved in maintaining water balance in the cornea?

A

Na+/K+ pump, Na+/Cl- cotransporter, water channels, K+ channels and H+ exchange/cotransport.

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19
Q

If the Na+/K+ pump were to be blocked, what would happen to the cornea?

A

it would become very cloudy.

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20
Q

What drives the Na+/Cl- cotransporter?

A

the Na+ gradient maintained by the Na+/K+ pump

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21
Q

K+ channels are under what type of control?

A

parasympathetic system.

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22
Q

K+ channels help control pH sensitivity by what?

A

as pH increases, K+ channels open and control the amount of water in epithelium.

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23
Q

pH in cornea is also regulated by what? these systems are under what type of control? (including the K+ channels)

A

lactate-H+ co transport and Na+/H+ exchange

parasympathetic control.

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24
Q

what type of water transport is used in the cornea? what is the water transport like in epithelium vs. endothelium?

A

aquaporin 5, water moving through the epithelium is much smaller compared to that of the endothelium.

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25
Q

corneal epithelium makes tears by doing what?

A

moving Cl- out and moving water with it.

26
Q

What two things stimulate K+ channels?

A
  1. mechano sensitive i.e. swelling of the cornea

2. pH

27
Q

In corneal epithelial wound healing, new basal cells originate from what type of cells and where?
Migration of new basal cells happens at what rate and where do they go?
basal cell division happens at what rate per day? which hypothesis is in support of this system?

A

stem cells at limbus and undergo mitosis.
123 um per week, toward the center of corneal epithelium, they then move upward and once at surface they can be sloughed off.
10-15%
XYZ: X (proliferation of basal cells) + Y (centripetal movement of cells) = Z (cells loss from surface).

28
Q

When we get an epithelium abrasion what happens?

A

mitosis stops. cells retract, thicken, loose hemidesmosomal attachments (causes haziness), enlarge. Once problem is fixed, mitosis resumes and attachments reform (start reforming within the first 18 hrs).

29
Q

If we get damage to the basement membrane in corneal epithelium what happens?

A

release of EGF, production of fibronectin to cover area, cytokines, integrins and laminins play a role in cell adhesion (these substances can get into stroma when there is damage which allows them to bind to keratocytes and initiate healing response).

30
Q

How many different types of collagen? how many of these are found in the eye?

A

30 types, 22 in eye.

31
Q

what type of collagen is found in sclera?

A

type 5 and type 1 (which are less than 5 nm in diameter).

32
Q

types of collagen normally found in basement membrane?

A

type 4 and 7

33
Q

What are two common theories of transparency? what is common amongst the two theories?

A
  1. destructive interference
  2. size theory (fibril size must be less than 30 nm and interfibril distance must be less than half the wavelength of light in order to maintain transparency).
    interfibril distance and regularity of fibrils is important.
34
Q

constructive interference causes what? destructive? what causes scattering in terms of light rays?

A

amplification
cancels out therefore no scattering.
when a light ray comes in, hits a cell and reflects back.

35
Q

What helps maintain fibril spacing in cornea?

A

PGs maintain separation of fibres.

36
Q

in corneal PGs what two types of sulphate are involved and what do they do?

A

keratan sulphate: regulates collagen fibre diameter.

dermatan sulphate: regulates interfibrillar spacing.

37
Q

GAGs stretch from what to what and help regulate?

A

one fibril to another and help maintain inter fibril separation.

38
Q

Loss of corneal transparency can be due to?

A

collagen abnormalties and its relationship to PGs.

39
Q

macular dystrophy is due to an abnormalty in what?

A

keratan sulphate synthesis. therefore no regulation of collagen fibre diameter.

40
Q

Cornea is what % hydrated? sclera?

A

80%, 70%

41
Q

How do PGs play a role in corneal hydration and transparency?

A

high concentration of GAGs increases in swelling pressure, which produces interfibril tension which maintains regular arrangement of fibres.

42
Q

to maintin cell regularity in the cornea (helps give transparency) the cornea must prevent what from happening?

A

water accumulation can cause swelling and disorganization of cells. this is achieved by water tight barriers and pumps.

43
Q

secretion of tears is stimulated by what?

A

sympathetic system.

44
Q

When acidification is high, this does what to the K+ channels?

A

increases amount of K+ going out through channels.

45
Q

chloride channels are under what control?

A

sympathetic innervation

46
Q

What transforms water into gel substance in cornea?

A

PGs

47
Q

What is the membrane potential across the corneal epithelium?

A

25mV

48
Q

how is the corneal stroma repaired with a wound occurs? What type of cells are involved and what are they activated by? what type of contractile cells are used and what do they commonly cause?

A

regeneration rather than fibrosis (we do NOT want scars forming, we cant see through scars)
keratocytes are used (specialized fibroblasts, non contractile) and they are activated by cytokines.
myofibroblasts they promote wound closure (associated with the haze)

49
Q

What type of cells are present in the corneal stroma that are involved in wound repair? (the non contractile ones) what are some unique properties?

A

keratocytes

remain dormant until required (i.e. corneal injury occurs) and they can produce crystallins (small proteins)

50
Q

what are the five stages of corneal stroma wound healing?

A
  1. activate: release of cytokines activate keratocytes
  2. cell death: keratocyte apoptosis or necrosis (peaks around 4 hrs, no immune response)
  3. proliferate: keratocyte proliferation (beings 12-24 hrs after injury)
  4. immune response: (arrival of monocytes etc 8-24 hrs after injury)
    (proliferate and immune happen around the same time)
  5. Regenerate: generation of activated keratocytes, fibroblasts and myofibroblasts (1-2 weeks after injury).
51
Q

after refractive surgeries, the cornea weakens and doesnt regain full strength for how long? haze would be due to? central incisions take how long compared to periphery? what also might delay healing?

A

around 4 years.
myofibroblasts
central cornea takes much longer to heal due to immune cells having to travel from periphery
steroids (they reduce inflammation therefore delay healing process)

52
Q

where would you find more pumps, corneal epithelium or endothelium? in the epithelium, water travels into the tear film by what? in the endothelium what does the water do?

A

endothelium.
in epithelium, water travels with Cl- into the tear film to produce tears
in endothelium water combines with CO2 to make HCO3- which will go into the aqueous humor in the AC (THIS DOES NOT FORM AHUMOR, THIS IS DONE BY CILIARY BODY).

53
Q

what pumps are present on the corneal endothelium membrane?

A 
Na+/K+ pump: maintains gradient, drives the next exchanger
Na+/H+ exchange, acidifies extracellular matrix
Na+/HCO3- co transporter
HCO3-/Cl- exchange
water channels (aquaporins present on both endo and epi membranes)
54
Q

What enzyme drives the production of HCO3- on the corneal endothelium membrane?

A

carbonic anhydrase

55
Q

transparency of the corneal endothelium depend on what two things?

A

temperature and leak/ion pump balance (remember pumps move ions NOT water however water mvoes with ions).

56
Q

corneal endothelial layer is what type of epithelium? does this layer divide? what would cause haziness during injury?

A

simple cuboidal.
NO, but cells can enlarge and spread hypertrophy when there is disease or cell loss (due to aging)
loss of pumps and tight junctions. pumps and junctions are restored with single layer is restored from hypertrophy.

57
Q

where does the cornea get most of its oxygen? where does the cornea get glucose, AA and vitamins?

A

atmosphere through tears.

mainly from aqueous (blood supply supplies aqueous).

58
Q

when people wear contact lenses, when the inflammatory response is stimulated, what does this inhibit? with prolonged corneal stress what can happen?

A

inhibition of Na+/K+ pumps causing the cornea to become cloudy
endothelial cells will enlarge.

59
Q

When people wear extended contact lenses what effects can this have?

A

epithelial thinning (mitosis rate decreases)
reduced O2 uptake
reduced intercellular hemi-desmosomes (result of prolonged edema)
decreased metabolic activity with hypoxia, effects barriers therefore increased risk of infections.

60
Q

vitamina A deficiency in the cornea can cause what? this is primarily seen in what age group? what is vit A important for?

A

keratinization of epithelial layer (epithelial cells becomes keratinized and the person can no longer see).
children
mucin production therefore with reduced mucin, we get reduced spreading of tears therefore dry eye.

Anatomy (18 decks)

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